This invention relates generally to the use of ceramic matrix composite (CMC) vanes, and more particularly, to CMC vane insulators and methods of use.
Gaps or seams may enable hot gases from the gas flow path of a gas or steam turbine to leak into un-cooled or unprotected vane components. To facilitate reducing gas flow through such gaps, at least some known turbines pressurize these gaps with compressor air, also called purge air, to cause a positive outflow from the vane into the hot gas flow path. However, directing purge air at the interface between the vane and metallic support structure may cause undesirably high stresses to develop on the vane which over time, may reduce the life expectancy of the CMC vane.
At least some gas or steam turbines use ceramic materials having a higher temperature capability than the metallic type materials. One specific class of such non-metallic low thermal expansion materials is ceramic matrix composite (CMC) materials which can endure significantly higher temperatures than metals and also require reduced cooling requirements that can be translated into increased engine efficiency and output. However, because of the substantial difference in coefficients of thermal expansion between CMC materials and supporting metallic structures, substantial thermal stresses may develop in the CMC material which may adversely affect the life and functionality of vanes fabricated from CMC materials.